Flea Larvae

The
second stage or cycle of flea development is the worm-like larvae. Fleas
go through what is called a complete metamorphosis: egg, larva, pupa, adult.
The female adult flea
lays numerous eggs; larvae emerge from the eggs and go through a series of
instars before pupating. Inside of the pupae (cocoon) the immature insect
is transformed into an adult flea. When transformation is complete,
surrounding conditions are right and nature signals that a host might be nearby,
the completely formed adult flea will emerge from the pupal casing - ready to
jump, feed, mate and continue the cycle. As a
group, the egg, larva and pupa are known as the immature stages of the flea.
As you become more familiar with this immature stage of the insect (as well as other
stages) you will have more information needed to effectively eliminate fleas
from your home and keep them from re-infesting the area. Flea
prevention is cheaper and far less time consuming than ridding your home of
thousands of hungry fleas.

Larvae hatch from their
eggs in as little time as 2 days and up to 14 days from the time they are laid
by the adult female. Temperature and humidity play major roles in this
timing. Temperatures between 80 and 90 degrees Fahrenheit and a relative
humidity of 70% or higher gives optimum conditions for the emergence of the
first stage or instar of larvae. Both eggs and larvae have very little
protection from drying out and have better survival rates in higher humidity
levels. They also avoid light, preferring areas such as beneath bedding
and furniture as well as behind baseboards inside the home; shaded areas of the
lawn are more likely to far more larvae than the sunny areas of the lawn.
(Flea larvae have no eyes but do respond to heat and light; they are easily desiccated,
as are flea eggs.) This is important information when understanding,
preventing flea larvae infestations or controlling flea
populations. Knowing where they usually
prefer to hide or feed helps in sanitation procedures as well as which control
products to use in most likely areas.

Desiccants
such as Drione Dust and Flea Stoppers take
advantage of the weaknesses of flea eggs and flea larvae. These products
easily dry out and kill soft, moist eggs and larvae. There are no baits
used to kill adult fleas but application of Flea Stoppers to carpets does, in a
sense, bait and kill their larvae. Fecal matter (larva food) is coated
with Flea Stoppers which in turn kills the larvae by ingestion. Simply
put, Flea Stoppers destroys flea eggs by drying them out; the material has two
modes of action on larvae: it dries them out and is also ingested as they
feed. Boric acid products (including borate
carpet treatments) have two modes of killing: desiccation and stomach
poison. Yet, when used properly, boric acid granules labeled for carpet
applications are actually safer than common table salt to mammals!

The
larvae break free from their egg shell with a little help from a small egg tooth
located on the head of the small worm. Newly hatched
flea larvae are usually about 1/4 inch long. This is the first instar or
stage of the larval development. Flea larvae go through three such instars
between hatching and pupating. Each instar is a little larger than its
preceding instar. Depending on availability of food and
optimum combination of heat and humidity, flea larvae can take from as little as
6 days and up to 2 weeks or more from egg emergence to the more dormant pupae
stage of the life cycle.
As this worm-like stage develops it will molt, leaving behind casings that
resemble the larvae. These casings are found in the vicinity of the larvae
since the immature stages of the flea are not nearly as mobile as their adult
counterparts. Both larvae and their empty casings (castings) are usually
found close to areas where flea hosts rest or frequent and are often found in
dirty pet bedding materials. They will also crawl under nearby beds,
furniture and behind baseboards as they search for debris and food and follow
their instinct to avoid light.
Flea larvae have no legs but do have a single row of hair-like bristles around
each segment of their body. These bristles aid in maneuvering, as do the
anal hairs. There are a total of 13 body segments - 3 thoracic and 10
abdominal sections.
Larvae have no eyes but they can still locate the adult fecal matter (dried
blood from the host animal) which flea larvae feed on for survival. Larvae
will feed on other types of organic debris but have best survival rate when they
feed primarily on dried blood. There are species of fleas whose larvae can
feed on certain dead animals for blood meals (instead of droppings of their
adult counterpart) but this is a rare occurrence that is not seen with cat
fleas. The blood meal of the cat flea larval stage is derived solely from
adult flea droppings which are made up entirely of undigested blood.
Coloration of newly hatched larvae is usually a creamy white. This color
changes as the larvae feed, changing to darker shades of yellow to brown.
Adult fleas, flea larvae and developed fleas that have not emerged from their
pupal casings all respond to vibrations. Vibrations (in combination with
movement, carbon dioxide, heat and humidity) will help developed fleas to emerge
from their pupal casing and adult fleas jump to find a warm blooded host.
The movement of dogs, cats, squirrels (and other hosts) causes flea eggs and
adult flea fecal material to fall in various areas close to the original
host. Flea larvae also respond to vibrations and movement, but in entirely
different ways.
Flea larvae have been known to fake death when they detect movement but their
most interesting behavior is clinging to certain when vibrations are felt.
As dogs or cats scratch the larvae picks up on the motion, wrapping itself
around the animal's hair. Larvae have also been noted to do the same thing
in carpet. When vacuum cleaners are close by, the larvae have been seen
clinging to carpet fibers - but they are not too successful. Vacuuming
usually picks up these larvae, despite their efforts.
As the end of the third instar larval stage draws near, flea larvae will begin to build the
pupal casing in which they will develop into fully developed adults. A
portion of the casing is made up of a silky material that is used to hold
together all other parts of the cocoon. Larvae gather debris from their
immediate surroundings with which they build their pupal case. Indoors,
the tiny bits of debris include animal hair, human hair, dust, lint and small
fibers of furniture, carpet and rugs. The materials used end up as the
perfect camouflage as they blend in with their surroundings. If we could
plainly see the pupae, they would be easier to locate and remove. Our only
choice is to vacuum thoroughly and regularly to remove as many of the pupae as
possible.
For more about the pupal stage, go to the flea pupae
information page.
By themselves, fleas are not as mobile as one would believe. Adult fleas
are designed for jumping (to locate and mount a warm blooded host) and crawling
forward through the fur of animals. The eggs easily fall off of an animal
as it moves. Flea larvae are capable of movement but do not stray far from
where they emerge from the eggs. Their food sources are very close by as
are the materials they need to spin and build their pupal casing. Warm
blooded, nesting animals not only serve as the food source but also as a source
of mobility, with adults, eggs and larvae food dropping off in various locations
frequented by their host. This dependence on the host for moving about
helps insure that the insect is scattered about an area. In nature's
scheme you will find many such examples of this "scattering of the
species" which helps insure the propagation of the species. Certain
spiders, ticks and fleas are examples of this phenomenon.

Understanding
the makeup, feeding and ability to create the perfect pupal casing exhibited by
the flea larvae should give you a better feel for the control or prevention of
flea populations. Knowing that the larvae are not very mobile helps narrow
down specific areas to include in the most important aspects of IPM for fleas:
inspection, sanitation and the safe use of proper pest control products.